Search My Oracle Blog

30 March, 2012

This is an undying myth. "datafiles are not updated when the database is in Hot Backup mode" .... "all updates are in the archivelogs and they are applied to the datafiles when the database is taken out of the Hot Backup mode" ... and so on ..

That was easy -- so far.
Now ... the question is : If I do a LIST BACKUP, what appears as the location of the datafile ? Is it /home/oacle/app/oracle/oradata/orcl ? OR is it /oradata/orcl ?
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Let's see ...........
.
.
.
.
.
.
.
.
.
.

Today's question :
What is the information that Oracle stores ? If the location of datafile 14 was under /home/oracle/app/oracle/oradata/orcl on 01-Jan and 23-Mar, why isn't that location presented ?Is it not stored in the repository ? Yes, the location of the BackupPiece is evident, but the location of the datafile is "current" even when the backup was taken when the datafile was elsewhere !

06 March, 2012

Jonathan Lewis has identified a seemingly simple example of a COUNT(*) query that can be written in two manners, has the same COST in an Explain Plan (although the Plan is different) and yet has very different actual performance characteristics.
(See Tom Kyte's explanation of how the two queries actual perform differently).
.
.
.